1. Field
The present invention relates to a specialized yttrium oxide comprising solid solution ceramic which is highly resistant to plasmas in general, particularly resistant to corrosive plasmas of the kind used in the etching of semiconductor substrates.
2. Description of the Background Art
This section describes background subject matter related to the disclosed embodiments of the present invention. There is no intention, either express or implied, that the background art discussed in this section legally constitutes prior art.
Corrosion (including erosion) resistance is a critical property for apparatus components and liners used in semiconductor processing chambers, where corrosive environments are present. Example of corrosive plasma environments include plasmas used for cleaning of processing apparatus and plasmas used to etch semiconductor substrates. Plasmas used for plasma-enhanced chemical vapor deposition processes often tend to be corrosive as well. This is especially true where high-energy plasma is present and combined with chemical reactivity to act upon the surface of components present in the environment. The reduced chemical reactivity of an apparatus component surface or of a liner surface is also an important property when corrosive gases alone are in contact with processing apparatus surfaces.
Process chambers and component apparatus present within processing chambers which are used in the fabrication of electronic devices and micro-electro-mechanical structures (MEMS) are frequently constructed from aluminum and aluminum alloys. Surfaces of a process chamber and component apparatus present within the chamber are frequently anodized to provide a degree of protection from the corrosive environment. However, the integrity of the anodization layer may be deteriorated by impurities in the aluminum or aluminum alloy, so that corrosion begins to occur early, shortening the life span of the protective coating. Ceramic coatings of various compositions have been used in place of the aluminum oxide layer mentioned above, and have been used over the surface of the anodized layer to improve the protection of the underlying aluminum-based materials. However, current materials used for protective layers deteriorate over time and eventually leave the aluminum alloy subject to attack by the plasma, even though the life span of the protective layer is extended over that of anodized aluminum.
Yttrium oxide is a ceramic material which has shown considerable promise in the protection of aluminum and aluminum alloy surfaces which are exposed to fluorine-containing plasmas of the kind used in the fabrication of semiconductor devices. A yttrium oxide coating has been used and applied over an anodized surface of a high purity aluminum alloy process chamber surface, or a process component surface, to produce excellent corrosion protection (e.g. U.S. Pat. No. 6,776,873 to Sun et al., mentioned above). In one application, the '873 Patent provides a processing chamber component resistant to a plasma including fluorine and oxygen species. The processing chamber component typically comprises: a high purity aluminum substrate, where particulates formed from mobile impurities present in the aluminum are carefully controlled to have a particular size distribution; an anodized coating on a surface of the high purity aluminum substrate; and, a protective coating comprising yttrium oxide overlying the anodized coating. The protective coating may include aluminum oxide up to about 10% by weight, and typically comprises 99.95% by weight or greater yttrium oxide. The protective coating is typically applied using a method such as spray coating, chemical vapor deposition, or physical vapor deposition.
U.S. Pat. No. 5,798,016, to Oehrlein et al., issued Aug. 25, 1998, describes the use of aluminum oxide as a coating layer for chamber walls or as a coating layer for a chamber liner. The Oehrlein et al. reference further discloses that since aluminum is reactive with a number of plasmas, it is recommended that “aluminum oxide or a coating thereof be disposed on the liner or chamber walls”, because aluminum oxide tends to be chemically inert. In addition, a protective coating may be applied over the surfaces of the liner and/or chamber walls. Examples which are given include Al2O3, Sc2O3, or Y2O3.
U.S. Patent Application Publication No. US 2001/0003271A1, of Otsuki, published Jun. 14, 2001, and subsequently abandoned, discloses a film of Al2O3, or Al2O3 and Y2O3, formed on an inner wall surface of the chamber and on those exposed surfaces of the members within the chamber which require a high corrosion resistance and insulating property. An example is given of a processing chamber where a base material of the chamber may be a ceramic material (Al2O3, SiO2, AlN, etc.), aluminum, or stainless steel, or other metal or metal alloy, which has a sprayed film over the base material. The film may be made of a compound of a III-B element of the periodic table, such as Y2O3 The film may substantially comprise Al2O3 and Y2O3. A sprayed film of yttrium-aluminum-garnet (YAG) is also mentioned. The sprayed film thickness is said to range from 50 μm to 300 μm.
In another application, a ceramic composition of matter comprising a ceramic compound (e.g. Al2O3) and an oxide of a Group IIIB metal (e.g. Y2O3) has been used for a dielectric window of a reactor chamber where substrates are processed in a plasma of a processing gas (e.g. U.S. Pat. No. 6,352,611, to Han et al., issued Mar. 5, 2002). The ceramic compound may be selected from silicon carbide, silicon nitride, boron carbide, boron nitride, aluminum nitride, aluminum oxide, and mixtures thereof; however, aluminum oxide is said to be available in a pure form which does not outgas. The Group IIIB metal may be selected from the group consisting of scandium, yttrium, the cerium subgroup, and the yttrium subgroup; however, yttrium is preferred, with the oxide being yttrium oxide. The preferred process for forming or producing the dielectric member is by thermal processing of a powdered raw mixture comprising the ceramic compound, the oxide of a Group IIIB metal, a suitable additive agent, and a suitable binder agent.
In another application, a protective coating for a semiconductor processing apparatus component is described. The protective coating comprises aluminum or an aluminum alloy, where the coating includes a material selected from, for example, but not limited to: yttrium-aluminum-garnet (YAG); an oxide of an element selected from the group consisting of Y, Sc, La, Ce, Eu, and Dy; a fluoride of an element selected from the group consisting of Y, Sc, La, Ce, Eu, and Dy; and combinations thereof is used (e.g. U.S. Pat. No. 8,087,607 B2 issued on Nov. 29, 2011, and entitled “Clean, Dense Yttrium Oxide Coating Protecting Semiconductor Apparatus”, mentioned above). The coating is applied to a substrate surface by thermal/flame spraying, plasma spraying, sputtering, or chemical vapor deposition (CVD). The coating is placed in compression by applying the coating at a substrate surface temperature of at least about 150-200° C.
The kinds of protective coatings described above have been used to protect exposed surfaces of a plasma source gas distribution plate of the kind used in semiconductor and MEMS processing apparatus. However, due to the concentration of reactive species which are present at the surface of the gas distribution plate, the lifetime of the gas distribution plate has typically been limited, from about 8 processing days to about 80 processing days, depending on the corrosivity of the plasma created in the processing chamber. To increase the lifetime of a component such as a gas distribution plate, a gas distribution plate was fabricated from a solid yttrium oxide-comprising substrate, as described in U.S. Pat. No. 7,479,304 B2 issued on Jan. 20, 2009 to Sun et al., and entitled: “Gas Distribution Plate Fabricated From A Solid Yttrium Oxide-Comprising Substrate”, mentioned above. The solid yttrium oxide-comprising substrate contains up to about 10% aluminum oxide in some instances. The solid yttrium oxide-comprising substrate typically comprises about 99.99% yttrium oxide.
As device geometry continues to shrink, the on-wafer defect requirements become more stringent, as particulate generation from apparatus within the processing chamber increases in importance. For plasma dry etch chambers running various halogen, oxygen, and nitrogen chemistries, such as F, Cl, Br, O, N, and various combinations thereof, for example, the selection of the material used for apparatus components and chamber liners becomes more critical. The materials with good plasma resistance performance (which also have adequate mechanical, electrical and thermal properties), can reduce particle generation, metal contamination, and provide prolonged component life. This translates to low costs of manufacturing, reduced wafer defects, increased lifetime, and increased mean time between cleaning. Ceramic materials which have been used in such applications include Al2O3, AlN, and SiC. However, the plasma resistance properties of these ceramic materials is not adequate in many instances, particularly when a fluorine plasma source gas is involved. The recent introduction of Y2O3 ceramic shows improved plasma resistance properties, but this material generally exhibits weak mechanical properties that limits its applications for general use in semiconductor processing components, processing kits, and chamber liners.